Generally, a spectacle lens is manufactured by a manufacturing side such as a lens maker based on order information obtained from an order-placement side such as a spectacle store, and provided to the order-placement side. In this case, there are two types for the lenses provided by the manufacturing side, namely one requiring an edging at the spectacle store and the others finished to be settable as it is to a frame without the need for the edging at the spectacle store. In the former case, the lens provided by the manufacturing side has optical surfaces of a curved surface shape satisfying an optical specification such as a diopter and the like on both the surfaces, while the outer shape thereof is still be a circle. The spectacle store, therefore, needs to measure an edge shape of the frame with a frame shape measurement device and edges the circular lens with an edger based on the measurement data, layout information, and the like to make the lens be settable in the frame.
In this regard, the latter case requires the spectacle store to simply set the lens in the frame. Hence, in recent years, the use of the lenses of the latter case is expanding gradually. As an example of the system that has realized the provision of the latter lens, for example, there is one disclosed in Patent Document 1. In the system disclosed in Patent document 1, information necessary to manufacture a lens such as three-dimensional frame shape information is transmitted to a manufacturing-side computer via an order-placement side computer; based on the information, a circular lens having an optical surface of a curved surface shape satisfying a predetermined optical specification is obtained at the manufacturing side; further, the circular lens is edged so that the finished lens has a shape settable in the frame; and the finished lens is supplied to the order-placement side.
Meanwhile, in this manufacturing system, in the step manufacturing the circular lens having the optical surface satisfying the predetermined optical specification, a semi-finished lens blank being a circular plastic material having an appropriate curved surface having an optical surface having a surface shape already satisfying a predetermined optical specification on one side but has no such optical surface satisfying the predetermined optical surface on the other side, is used. In other words, many types of semi-finished lens blanks of which one surfaces satisfy a variety of optical specifications are prepared in advance, and a semi-finished lens blank having the optical surface satisfying the optical specification of an received order is selectively determined. Then, the other surface is processed with a curve generator or the like to form an optical surface of a predetermined surface shape, thereby the circular lens satisfying the predetermined optical specification is obtained.
Incidentally, to be more precise, the semi-finished lens blank is manufactured in the following manner. For instance, in the case of using a thermosetting resin material as a lens material, a molding method called a casting method is commonly employed, in which a casting mold is formed by two pieces of shaping dies having a predetermined curvature and a sealant (for example, gasket), and a lens material is injected thereinto to go through polymerizing, curing, and mold-releasing to be mold. At this time, the previously-described shaping die (upper die: the convex surface side of a product) is shaped to have a coverture forming an optical surface of a curved surface shape satisfying a prescription, and the surface therefore satisfies specification as a finished surface, so that a grinding and polishing is performed on the concave surface side so as to satisfy a prescribed diopter. This processing system making use of the semi-blank has an advantage in that the delivery time from the order receipt to the shipment can be reduced because the processing is required only for a single surface.
Further, in this manufacturing system, after the circular lens is obtained, it is required to edge the lens to finish the lens to be a spectacle lens of a shape settable to a frame to thereby provide to the order-placement side. The edging is performed in the following manner. Specifically, first, the position of the edge shape in the circular lens is defined to perform the edging. This position is inevitably defined when assuming a spectacle lens shape that satisfies the specification when set in the frame under conditions set by circular lens shape information, three-dimensional edge shape information, prescription information, and the like. An important point in this case is a circular center of the circular lens, specifically, a geometric center of the edge shape is arranged with a shift to the extent of a so-called eccentric quantity with respect to an optical center formed at the geometric center of the circle. This is conducted with an aim of matching the position of a spectacle lens that the line of sight passes through with the optical center of the lens when the spectacle lens is worn by a person. The position that the line of sight passes through generally shifts by a predetermined distance inward from the geometric center of the edge. This shifted quantity is generally called an eccentric quantity. Therefore, in order to define the edge in the circular lens, the definition is made by shifting the geometric center of the edge shape by an eccentric quantity with respect to the center of the circular lens.
[Patent document 1]    Japanese Patent Publication No. 2982991